Viruses Strategies for control of influenza and other respiratory infections have been based on models using assumptions derived from the Tecumseh Study of Respiratory Illness, conducted 30 years ago. Since that time, laboratory and analytic methods have markedly advanced. We have recruited more than 300 households with children for a longitudinal study of respiratory illnesses. We propose to determine the incidence and characteristics of respiratory infections by collecting specimens from subjects with respiratory illness meeting a case definition, and testing specimens using PCR to identify influenza and other respiratory viruses. To determine susceptibility to influenza, and immunologic response to infection and vaccination, blood specimens will be collected at three points annually, and tested in hemagglutination inhibition (HAI), microneutralization and other assays to measure influenza specific antibody titers and changes in titers between specimens. Both standard techniques and dynamic transmission models will be used in data analysis. Household infection rates and the effects of crowding and humidity will be determined. Secondary spread, conditioned on susceptibility will be calculated. Transmission in schools and the overall community will be compared with those in the household. Results will provide an updated scientific basis for determining control strategies.